Long-term objectives are to develop new antitumor deoxynucleoside analogs and to improve the clinical effect of the nucleoside analogs currently useful in cancer chemotherapy. Two approaches are taken, the first appeoach is a study the properties of the enzymes involved in DNA and nucleotide metabolism and then to examine the affect of active analogs and their metabolic derivatives on those enzymes. This enzyme data together with the study of these analogs in cell culture, will enable us to understand more the mode of action, the metabolism, and the biochemical determinants of these analogs. Once this is known an attempt will be made to modify these deteminants to make the cells more susceptible or resistant to these agents. The information thus obtained will be useful to Clinicans in establishing new protocols and in choosing the most appropriate anti-cancer agents. The second approach is to study the enzymatic activity profiles of tumor cells taken from patients with respect to the DNA and nucleotide metabolizing enzymes. These studies will provide some insight into the mechanism of susceptibility and resistance of the currently used nucleoside analogs. Based on thses leads compounds which are uniquely ometabolized could be designed and developed to destroy tumor cells with unique enzymatic profiles. These compounds would ultimately be used in the clinic with a more selective action. Specific Aims of this proposal are (1) Purification and Characterization of Ribonucleotide Reductase of Parental and Hydroxyurea resistant KB cells. (2) Purification and Characterization of DNA toposomerases. (3) Utilization of highly purified human enzymes or nuclei system in studing the mode of action of active deoxynudleoside analogs or their phosphorylated derivatives. (4) Study of the activity, and the mechanism of action of some TdR and CdR analogs in cloned human cell lines with different sensitivity to AraC and Hydroxyurea. (5) Study of the activity of CdR deaminase and TdR kinase in tumor cells from patients and cells grown in culture by developing and employing. Monoclonal antibodies against TdR kinase, and CdR deaminase.